The present invention relates to an optical disk apparatus for moving a light beam spot irradiated from an optical head to a target track of a disk medium surface by a seek control and, more particularly, to an optical disk apparatus and its seek control method in which a deceleration control when the optical head approaches a target track is optimized.
Hitherto, according to an optical disk apparatus, an optical head is mounted on a carriage that is moved in the radial direction of a disk medium by a voice coil motor. The optical head converges a laser beam by an objective lens and forms a micro beam spot onto the medium surface. The objective lens is driven by a lens actuator and moves the beam spot in the disk radial direction. A range in which the beam spot can be moved by a lens actuator is so narrow to be, for example, 32 tracks on one side. A movement of the beam spot exceeding 32 tracks is executed by the carriage.
When a seek command is received from an upper apparatus, the optical disk apparatus executes a seek control for moving the beam spot of the optical head to a track address received as a command parameter. The seek control is mainly divided into a coarse control to mainly move the carriage, a fine control to mainly move the lens actuator, and a deceleration control to set the speed to zero at a target track. As for those controls and switching operation, when the number of remaining tracks (difference) for the target track exceeds, for example, 32 tracks, the coarse control is executed and, when the number of remaining tracks is equal to or less than 32 tracks, the fine control is executed. In a state in which the on-track control of the lens actuator is released, the coarse control and fine control execute the speed control based on a predetermined target speed table. During the speed control, the number of tracks over which the head has passed is known from a zero-cross detection signal of the tracking error signal and the number of remaining tracks up to the target track is monitored. When the number of remaining tracks reaches a specified value, the deceleration control is performed. At the end time point of the deceleration control, ideally, the beam spot of the optical head reaches the target track and the speed is zero.
When the deceleration control is finished, a control mode of the lens actuator is switched to a position control of the target track and a servo pull-in to pull in the beam spot to the target track is performed. In the deceleration control, so long as a deceleration and an acceleration of the lens actuator has already been known, a deceleration start position in front of the target track is obtained and an ideal deceleration control can be performed.
In such a seek control of the conventional optical disk apparatus, an acceleration of the lens actuator is determined at the stage of the design, a predetermined acceleration is set commonly for all of the apparatuses, and the deceleration control is executed. In the actual apparatus, however, the lens actuator of the optical head has an acceleration that is peculiar to the apparatus due to an acceleration performance peculiar to the lens actuator, a coil current, an eccentricity of the medium, a difference of an assembly state, a fluctuation of dimensions (obviously, within a permission precision), or the like although such an acceleration lies within a range of the acceleration performance which is required at the design stage. Therefore, in the fixedly decided acceleration, the acceleration performance peculiar to the apparatus is not considered. There are problems such that when there is a large fluctuation, the deceleration control is insufficient or, contrarily, the deceleration control is excessively executed and the pull-in to the target track fails and the seek performance deteriorates due to a retry in association with a seek error.